I have been meaning to write up a short post about this for a while, but thanks to the start of a new school term I have been a bit busy.
If you have seen the security news in the last month or so you will know that RSA-768, a 768bit or 232 decimal digit asymmetric key, has been broken (factored). This has important security repercussions for all of us because it is these public key algorithms like RSA, or ElGamal, that guard our online transactions, and e-mail conversations.
So just how much should we be worrying about this newest ‘break’?
When it comes to public key cryptography it is important to remember that their security is essentially in our inability to factor them quickly. The only real way that public key cryptography could be considered broken is if we find a way to drastically increase our ability to factor massive prime numbers. Thankfully that time is still far away. In fact after digging into the news articles a little more it quickly became obvious that the feat of factoring a 768bit key, while incredibly difficult, was inevitable.
So what now?
Nothing. Currently the most popular asymmetric key size in use is 1024bit, which represents a work load increase of over 1000 times when compared to RSA-768. Still afraid? Check out the list of RSA challenges that have been issued over the years and just how few have actually be ‘broken’.
In choosing my current PGP/GPG public key I decided to go with a 2048bit one, which, according to all accounts, will be safe for years to come. As always, I recommend checking out this site for the most up to date key length recommendations from the world’s foremost cryptography experts.
There you have it
With the knowledge that you’re online transactions are still perfectly safe you have nothing to worry about.
For reference, the currently recommended key lengths for asymmetric encryption algorithms, like RSA, are 1976bit (BSI recommendation for use after 2016), 2048bit (NSA recommendation for current and future use), and 2432 (ECRYPT II recommendation for protection until at least 2030).